1. Field of the Invention
The present invention relates to a Raman microprobe apparatus for determining crystal orientation by utilizing polarization selective Raman microprobe spectroscopy, and more particularly to improvements in simplicity and accuracy of the apparatus.
2. Description of the Prior Art
Raman microprobe determination of cyrstal orientation is described, e.g., in J. Appl. Phys., Vol. 59, 1986, pp. 1103-1110 by J. B. Hopkins et al.
Referring to FIG. 1, there is schematically illustrated an arrangement of a principal portion in a conventional Raman microprobe apparatus for determining crystal orientation. An incident beam 1a of circularly polarized light is converted into a linearly polarized light beam 16 by a polarizer 7 which can be rotated. The linearly polarized light beam 1b is deflected by a half mirror 5 and then a light beam 1c thus deflected is focused on a specimen 4 by an object lens system 3.
Raman light scattered from the specimen 4 is collected as a Raman light beam 2a by the object lens system 3, a half of which is transmitted as a beam 2b through the half mirror 5 and then deflected as a beam 2c toward a polarization analyzer 8 by a complete mirror 6. A Raman light beam 2d having a particular polarization plane is selected from the beam 2c by the polarization analyzer 8.
The polarization-selected Raman light beam 2d is then introduced into a spectrometer (not shown) and then the Raman band of the specimen 4 is measured. In the conventional apparatus, the polarization intensity characteristic of the selected Raman light 2d is measured with either the polarizer 7 or polarization analyzer 8 being fixed and the other being rotated by degrees. The measured data of the polarization intensity characteristic are processed by a computer and compared with data derived theoretically as to known crystal orientation, whereby the crystal orientation of the specimen 4 can be determined.
In the conventional apparatus, however, it is difficult to make correction for a measured data which contains experimental errors due to polarization plane shifts and light intensity distribution changes at the half mirror 5 and complete mirror 6.
In FIG. 1, linearly polarized light 1b having a particular polarization angle is selected by the polarization 7 from circularly polarized incident light 1a. This linearly polarized light 1b is reflected by the half mirror 5 and then slightly changes to linearly polarized light 1c having a polarization angle and intensity distribution both shifted a little from those of the light 1b. As well known, the reason is that the reflectance of a mirror changes depending on the polarization angle of light. Since the Raman scattering is excited by the polarized light 1c slightly different from the polarized light 1b, it is necessary to make correction as to an error in the measured data which is caused by the difference between the light 1b and the light 1c.
When Raman light 2a is transmitted through the half mirror 5, it also changes to light 2b having slightly different polarization components and slightly different intensity distribution. Further, when the light 2b is reflected by the complete mirror 6, it slightly changes to light 2c. A polarization angle and intensity distribution of linearly polarized light 2d selected from the light 2c are slightly different from those of the Raman light just as scattered from the specimen 4. Therefore, it is also necessary to make correction as to errors in the measured data which is caused by the polarization angle shifts and intensity distribution changes in the Raman light at the half mirror 5 and the complete mirror 6.
As described above, it is necessary in the conventional apparatus to make correction for the measured data as to the polarization shifts in both the incident light and Raman light. However, since it is difficult to separate the errors in the obtained data due to the respective polarization shifts in the incident light and the Raman light, it is compelled to make averaged correction. Therefore, some error still remains in the corrected data, and the accurate value can not be known.
Further, since the measurements are carried out with either the polarizer 7 or polarization analyzer 8 being rotated and the other being fixed in the conventional apparatus, not only the two optical parts of the polarizer and analyzer but also a parameter representing the analyzer relation between the polarizer and analyzer is indispensable.